Many industries utilize tubing to dispense fluid or remove fluid. For example, in the medical industry, tubing is used to deliver fluid containing nutrients or medication to patients. Tubing can also be used in medical applications to remove fluid from patients and to drain fluid produced during some procedures. In certain applications, a specified amount of fluid is expected to be delivered or removed over a particular period of time.
In many cases, the medical and pharmaceutical industries utilize silicone tubing for the delivery and removal of fluids because silicone tubing is non-toxic, flexible, thermally stable, has low chemical reactivity, and can be produced in a variety of sizes when compared with tubing made from other materials. For example, silicone tubing may be used with enteral pumps and infusion pumps to provide nutrients, medication, fluids, and the like to patients.
Medical devices utilizing silicone tubing are expected to deliver or remove fluids at a specified rate. To illustrate, an enteral pump can be expected to deliver a selected amount of nutritional fluid to a patient in a particular period of time, such as 50 mL/hour. The dimensions of the silicone tubing coupled to medical devices can affect the flow rate of fluid pumped by the devices. Consequently, medical and pharmaceutical industries would benefit from cost effective tubing solutions that provide a high level of dimensional accuracy.
Typically, silicone tubing is formed by one of two processes, extrusion or molding. During extrusion, a flowable raw material is forced through a die and is then solidified. Existing extrusion processes have limited process control, and while they can achieve limited lengths of dimensionally accurate tubing, extended runs cannot be achieved.
Another approach to tube formation is molding. However, molded tubes have physical artifacts that can be undesirable, such as parting lines and/or knit lines that form when mold components meet. Additionally, the processes used to form molded tubes can be expensive and lack flexibility. Accordingly, manufacturers of tubing can be reluctant to utilize molding processes to produce silicone tubing due to the expense and lack of flexibility of these processes and/or the undesirable appearance of visible artifacts produced by these processes. Additionally, molding cannot generally form long lengths of tubing, such as on the order of several meters and above.
Some previous attempts to provide dimensionally accurate tubing are described in the following patents and patent applications.
US Patent Application Publication No. 2001/0022411 describes catheters or other structures, such as hoses, balloons, etc., that are formed by immersing a mandrel into a number of baths. The structures can be made of silicone rubber and may have multiple layers. This application describes catheters having an overcoat layer with a preferred thickness of 0.35 mm±0.06 mm (0.0175 in.±0.0025 in.) and preferred inner layer dimensions of 0.89 mm±0.1 mm (0.035 in.±0.004 in.).
US Patent Application Publication No. 2003/0030165 describes medical catheters and tubing that are produced for intravascular procedures. The materials are preferably thermoplastics. Proximal and distal portions of the tubing have a differing stiffness and may be formed from different materials. The catheters are formed through extrusion with a melt pump that is preferably a displacement pump. Outside diameters of the tubing are to be minimized while maximizing the inside diameter. Desired dimensional tolerances for the inside diameter are about 0.0005 inches and about 0.001 inches for the outside diameter.
US Patent Application Publication No. 2003/0132552 describes tubing formed from a system that compares measured dimensions against stored target dimensions to generate feedback to adjust process variables. The melt is composed of a thermally extrudable material. Error tolerances of ±1 micron are based on the number of measurements taken by a laser gauge per second and the extrusion speed.
US Patent Application Publication No. 2006/0255497 describes thermoplastic tubing formed from an extrusion process. Tolerances for the tubing are produced by exerting pressure on the tube using rollers situated at an entry to a sizing device. A fluctuation in thickness is described as 0.1 mm for a tube having a diameter of 100 mm.
US Patent Application Publication No. 2011/0005661 describes medical tubing formed from a number of ring-shaped elements that are fused together. The process includes wrapping a stainless steel wire around a mandrel. A silicone tube may be placed around the wound coil outer diameter. Tolerances on the inner diameter can be held to 0.001 in. or less with a comparable tolerance for the outer diameter. The inner diameter may be from 0.026 in. to 0.75 in.
U.S. Pat. No. 5,759,647 describes a tubular article formed by injection molding a thermoplastic synthetic resin. The tube may have a length from several cm to more than one meter and a wall thickness ranging from less than one mm to several cm. In some cases, tubes can have a wall thickness of 2 mm with a maximum difference of wall thickness of 0.1 mm or 0.2 mm.
U.S. Pat. No. 6,508,972 describes rubber tubing formed via extrusion with a gear pump. The tubing is cut to form gaskets. A goal of the system is to produce a gasket with outer diameters and inner diameters deviating by ±0.005 in.
U.S. Pat. No. 5,948,332 describes thermoplastic material extruded to form tubing. Heating elements are provided that modify the temperature of the tubing during the extrusion process. The regulation of the temperature can exert a particular pressure on the tubing as it moves over the mandrel to produce a preferably uniform wall thickness.
U.S. Pat. No. 5,820,607 describes a multilayered tube having a hollow inner layer surrounded by a pharmacologically active substance. One or more of the layers may comprise silicone. The pharmacologically active substance may be suspended in one layer and migrate to the outer surface of the tube, the inner surface of the tube, or both. The tube may be extruded or molded and control of the overall diameter of the device is preferred. Examples of outer diameters include 3.175 mm and 1.7 mm, examples of inner diameters include 1.981 mm and 0.8 mm, and examples of layer thickness range from 0.1 mm to 3 mm.
US Patent Application Publication No. 2008/0248226 describes multi-layered tubes that are formed with a heat-shrinkable fluoropolymer liner and extruding an elastomeric cover, such as a cover having a silicone formulation, over the liner. The liners are paste extruded. A total thickness of the tube may be between 3 mils to about 50 mils and a thickness of the liner can be between 1 mil to about 20 mils The tubes are tested for length of life and tensile modulus.
Although some of the above-described documents describe a desired tolerance for certain dimensions, the prior art does not fully enable a high level of process control. Additionally, the technologies described in the foregoing prior art documents do not achieve certain dimensional tolerances over extended lengths of tubing or with respect to a specified number of tubes, and certainly not over extended lengths of tubing or tube segments therefrom.
The use of the same reference symbols in different drawings indicates similar or identical items.